Sound pressure level (SPL) calculator
Enter the RMS sound pressure to get its level in decibels. Used by audio engineers and anyone reading microphone specs.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter rms sound pressure.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Lp = 20 × log₁₀(p / p₀), where p₀ = 20 µPa is the reference pressure in air.
Example
Inputs: RMS sound pressure = 1 Pa. Result: Sound pressure level: 93.98 dB SPL; Ratio to reference: 50,000.
Limits and caveats
- Enter the RMS value, not the peak. For a sine wave RMS equals the peak divided by √2.
- The 20 µPa reference is for air; underwater acoustics usually uses 1 µPa.
Questions about this tool
Why multiply by 20 and not 10?
Intensity is proportional to pressure squared, so 10 × log of the square equals 20 × log of the pressure.
What level is 1 pascal?
About 94 dB SPL, the level used to calibrate microphones.
Is this dB(A)?
No, it is unweighted. dB(A) applies a filter that mimics the ear's sensitivity.